[neilep (OP)]

Dearest Photonologists,


As a sheepy I of course propel myself through space all the time with my TEMU purchased solar sail

Look here I am in this bona-fide non doctored true picture.




Me being propelled by my TEMU solar sail just moments ago !




If photons are massless, how do solar sails still manage to generate propulsion? What fundamental physics allows light, without mass, to exert a continuous propulsive force on a spacecraft?

I reached out to Rod Stewart but he was too busy sailing !

do ewe know ?

whajafink ?


Hugs et les shmishes


mwah mwah mwah

neil
xxxxx

[Halc]

If photons are massless, how do solar sails still manage to generate propulsion? What fundamental physics allows light, without mass, to exert a continuous propulsive force on a spacecraft?

Because photons, despite lack of rest mass, have momentum, and it's exchange of momentum that gives thrust to a solar sail.

[neilep (OP)]

If photons are massless, how do solar sails still manage to generate propulsion? What fundamental physics allows light, without mass, to exert a continuous propulsive force on a spacecraft?

Because photons, despite lack of rest mass, have momentum, and it's exchange of momentum that gives thrust to a solar sail.

Thank you Halcy....still confused a little....if the photon has no mass then where does the momentum come from ?

[A-wal]

Thank you Halcy....still confused a little....if the photon has no mass then where does the momentum come from ?

My very non-technical way of looking at it, light has no mass but overall energy is mass+momentum so in the case of photons just momentum. When they hit the sail they stop moving so the energy is transferred to the sail.

[Halc]

Thank you Halcy....still confused a little....if the photon has no mass then where does the momentum come from ?

Momentum is γmv which is singular (∞ * 0, which is undefined) for a photon, so inapplicable.
The momentum of a photon is h/λ (Planck constant / wavelength), which is not singular.

light has no mass but overall energy is mass+momentum so ...

Adding zero (mass) to anything is pointless, and energy and momentum are different things with different units, but yes, energy can be expressed as hc/λ. That says that energy is proportional to momentum for massless things like photons, and is the same numeric value if using natural units where c is 1.

[Janus]

If photons are massless, how do solar sails still manage to generate propulsion? What fundamental physics allows light, without mass, to exert a continuous propulsive force on a spacecraft?

Because photons, despite lack of rest mass, have momentum, and it's exchange of momentum that gives thrust to a solar sail.

Thank you Halcy....still confused a little....if the photon has no mass then where does the momentum come from ?

Its energy.  The idea that momentum can only be associated with mass was found to be incorrect over a hundred years ago.

[alancalverd]

One derivation is ascribed to Einstein. Essentially a matter of dimensional analysis, which shows that a change in energy density is equivalent to a transfer of momentum.